1. Field of the Invention
The present invention relates to a mouthguard composition for preventing teeth and their surrounding oral tissues from a trauma occurred in a sport and so on.
2. Description of the Conventional Art
In contact sports such as rugby football and American football, a large external force may be applied to a head during the game. In order to confine a trauma on teeth and their surrounding oral tissues occurred at that time to the minimum, a mouthguard made of a rubber material, or an appliance called as a mouth protector or the like, is set in an oral cavity, thereby protecting the teeth and their surrounding oral tissues from the external force.
For the mouthguard, various materials are employed. Those that are most widely used at the present time are polyolefin rubbers and ethylene-vinyl acetate copolymers. In addition, a mouthguard comprising an ethylene-vinyl acetate copolymer having a thermoplastic polycaprolactone added thereto, as disclosed in Japanese Patent No. 2,594,830, is used.
However, in mouthguards prepared from such a material, when a large occlusal force is applied, the materials themselves are liable to be broken so that these mouthguards could be used only a few times. In particular, in a so-called xe2x80x9ccustom-madexe2x80x9d mouthguard that a dentist makes according to the shape of an oral cavity of an individual for whom the mouthguard is set, it is required to have durability from the economic standpoint. Accordingly, it was a problem that the mouthguard was broken within a comparatively short period of time and could be no longer used.
Further, in order to get a necessary impact absorption force, the conventional mouthguards are required such that their thickness is made thick. When such thick mouthguard is set in the oral cavity, the occlusion site rises from the usual site, whereby not only the setting feeling was unpleasant, but also the jaw oral cavity was likely adversely affected.
As a matter of course, since the shape of the oral cavity is different one by one, it is necessary to prepare and adjust the mouthguard according to the individual. For this reason, the preparation and adjustment of the mouthguard are generally carried out by heating and softening a material at approximately 80xc2x0 C. At this time, the conventional mouthguards are liable to be sticky to gypsum model or hands and fingers of an operator to be used for the preparation and adjustment. Thus, it has been demanded to realize a material for mouthguard that is less sticky.
The present invention is aimed to provide a mouthguard composition having high durability and impact absorption, which is free from sticking to gypsum model or hands and fingers at the time of preparation and adjustment works.
We, the present inventors, paid attention to a styrene block copolymer that is superior in tear strength to the conventional ethylene-vinyl acetate copolymers or polyolefin rubber materials. As a result, they have completed a mouthguard composition according to the present invention, in which the styrene block copolymer is added with an alicyclic saturated hydrocarbon resin and/or an ester gum for the purpose of imparting impact absorption and softening characteristics at low temperatures required for the mouthguard and further with an organopolysiloxane in which at least one of organic groups directly bound to the silicon atom in one molecule thereof is a phenyl group, a methylstyryl group, or an alkyl group having from 7 to 3 0carbon atoms for the purpose of reducing the stickiness at the time of works.
Specifically, the mouthguard composition according to the present invention comprises:
(a) from 40 to 80% by weight of a styrene block copolymer,
(b) from 20 to 60% by weight of an alicyclic saturated hydrocarbon resin and/or an ester gum, and
(c) from 0.1 to 10% by weight of an organopolysiloxane in which at least one of organic groups directly bound to the silicon atom in one molecule thereof is a phenyl group, a methylstyryl group, or an alkyl group having from 7 to 30 carbon atoms.
The styrene block copolymer as the component (a) of the present invention is a component as a basis for imparting durability and elasticity to the mouthguard. Examples of the styrene block copolymer that can be used in the present invention include a block copolymer of polystyrene and polybutadiene, a block copolymer of polystyrene and polyisoprene, and a block copolymer of polystyrene and a polyolefin. Of these is mostly preferable the block copolymer of polystyrene and a polyolefin from the reasons including the hardness and softening temperature required as the mouthguard. It is necessary that the content of this styrene block copolymer in the mouthguard composition is in the range of from 40 to 80% by weight. When the content of the styrene block copolymer is less than 40% by weight, the hardness as the mouthguard is insufficient. On the other hand, when it exceeds 80% by weight, the softening temperature of the mouthguard composition rises so that the preparation and adjustment are difficult.
The alicyclic saturated hydrocarbon resin and/or the ester gum as the component (b) of this invention is a component having effects for not only improving the impact absorption of the mouthguard but also lowering the softening temperature to make the preparation and adjustment easy. Though a number average molecular weight of the alicyclic saturated hydrocarbon that can be used in the present invention is generally from 500 to 900, it is most preferably from 550 to 650 for the purpose of controlling the softening temperature to a proper extent. On the other hand, as the ester gum, one prepared by esterifying rosin with glycerin is generally used, but one prepared by esterifying hydrogenated rosin with glycerin can also be used. The alicyclic saturated hydrocarbon resin and the ester gum can be used singly or in admixture, and the content thereof in the mouthguard composition is required to be from 20 to 60% by weight. When the content of the component (b) is less than 20% by weight, the impact absorption is not sufficient, and the softening temperature becomes higher, so that the preparation is difficult. On the other hand, when it exceeds 60% by weight, the resulting product is liable to be deformed by occlusal force, leading to a reduction in the durability of the mouthguard.
The organopolysiloxane in which at least one of organic groups directly bound to the silicon atom in one molecule thereof is a phenyl group, a methylstyryl group, or an alkyl group having from 7 to 30 carbon atoms as the component (c) of the present invention has an effect for reducing the stickiness to gypsum model or hands and fingers occurred during the preparation and adjustment of the mouthguard. Representative examples of the organopolysiloxane in which at least one of organic groups directly bound to the silicon atom in one molecule thereof is a phenyl group, a methylstyryl group, or an alkyl group having from 7 to 30 carbon atoms that can be used in the present invention include methylphenyl dimethylpolysiloxane, methylstyryl-modified dimethylpolysiloxane, and dimethylpolysiloxane modified with an alkyl group having 8 carbon atoms. The amount of the component (c) to be compounded in the mouthguard composition is required to be from 0.1 to 10% by weight. When the amount of the component (c) is less than 0.1% by weight, the effect for preventing the stickiness to gyp sum model or hands and fingers during the preparation and adjustment is not sufficient. On the other hand, when it exceeds 10% by weight, the component (c) bleeds out from the surface of the mouthguard, and the deformation of the mouthguard or the like is liable to occur.
In addition, the mouthguard composition according to the present invention may be added with an inorganic or organic coloring agent, a bactericide, an ultraviolet light absorber, etc. so far as the characteristics are not lost.